Conventional optical storage devices typically employ a single optical disk having a single recording surface for storing information. Use of a single disk allows the optical components, such as a mirror and a lens, to be arranged relative to the recording surface in a manner that optimizes the size and cost of the device. Although this results in a low-cost device having a relatively small form factor, its storage capacity is limited to that provided by a single surface. Commonly assigned U.S. Pat. No. 5,452,283, to Lee et al., entitled, LENS/MIRROR TOWER FOR AN OPTICAL STORAGE DEVICE, describes a multiple-surface system in which the beam from a single laser is steered by a stationary galvanometer-rotated mirror to optical heads associated with the respective recording surfaces. The heads are mounted on a carriage that moves them radially over the surfaces for access to selected data tracks on the surfaces.
Specifically, the rotating mirror selectively directs the beam to one of a vertical array of uniquely oriented deflection mirrors. When a deflection mirror receives the beam, it reflects it along a plane parallel to and close to a corresponding disk surface. The beam then passes through an imaging lens on the way to a 45.degree. mirror that redirects the beam radially toward an objective lens in the optical head associated with that surface. The objective lens, in turn, converges the beam on a small spot on the selected data track.
Therefore, it is apparent that the mirrors and lenses must be precisely aligned. Moreover, they must occupy a small space so that the form factor for the overall system is comparable with that of conventional multiple-disk, magnetic disk drives. Further, the lens and mirror optical components must be manufacturable within the cost constraints of the conventional single-disk optical components.
Various fabrication techniques might be employed to produce a multiple lens and mirror arrangement. One approach involves the construction of two separate components: a multiple mirror component and a multiple lens component. However, the cost of these parts, particularly the lens elements, is relatively high. Fabrication of the separate components entails individual assembly, including discrete adjustment and bonding, of each mirror element and each lens element onto respective portions of a precast housing. Moreover, some of the lenses must overlap because of the close proximity of the associated recording disk surfaces. This requires truncation of lenses and fitting together of the truncated lenses, a costly procedure. The assembly process further necessitates manual alignment of the mirror and lens components relative to each other.
An alternative approach involves plastic molding of an integrated lens/mirror unit. Although this process provides a low-cost unit, current molding technology typically cannot provide the level of wavelength quality needed for the mirror elements. This deficiency further causes stress in the plastic substrate material and leads to birefringence of the optical beam when passing through substrate, thereby degrading the accuracy and reliability of the component.
Therefore, it is desirable to provide a reliable, lens/mirror tower for use in a multiple-disk, optical storage device.
Specifically, it is desirable to provide a tower in which the optical elements are precisely configured and positioned so that the tower can be used in a multiple-disk optical storage system.
It is also desirable to provide a low-cost method for producing such lens/mirror towers.
In addition, it is desirable to provide a fabrication process that enables installation of mass produced lens/mirror towers in an optical storage device without further alignment of the lens/mirror elements.